In the medical endoscope, a demand for an objective optical system capable of magnifying observation for making precise diagnosis of a lesion is increasing.
Examples of the objective optical system having such a magnifying function include an objective optical system capable of switching between a normal observation state and a magnifying observation state by moving a moving lens group along an optical axis disclosed in PTL 1 to PTL 4, for example.
In order to perform magnification in the objective optical system capable of magnifying observation, at least one lens group needs to be moved. In such an objective optical system, in order to facilitate a focusing operation involved in magnification, it is preferable that a stroke of the moving lens group be ensured to be long, and magnification be performed gently.
Moreover, size reduction of an image pickup device has progressed in response to a demand for size reduction of endoscopes, and a small-sized image pickup device with a shading characteristic optimized in accordance with an incident angle of an off-axis principal ray has been provided, and a small-sized endoscope capable of magnifying observation is in demand.